AC-AC power converters are used in a wide range of applications, most commonly in motor drives. The topology of a standard converter, which converts AC to DC and then back to AC, consists of a rectifier 51, a pulse width modulation (PWM) inverter 52, and a DC filter capacitor 53, as shown in FIG. 1. In recent years, the increased attention on energy efficiency has spurred the development of matrix converters. The main circuit of a matrix converter, illustrated in FIG. 2, is composed of an input filter (not shown) and nine bidirectional switches 61, also known as bilateral switches. The matrix converter has a number of advantages over the standard converter. Matrix conversion directly converts AC to AC, thus eliminating the need for a large DC filter capacitor. The matrix converter is composed of a set of bidirectional switches, thus permitting both generation and motoring using the same set of switches. Further, the matrix converter permits an optimized power factor and harmonic content of input currents and three-level voltage switching for reduced voltage stress.
The bidirectional switches used in power converters such as matrix converters optimally have low loss, low on-resistance, fast switching times, and often must be able to withstand large voltages, typically 600-1200V. In some embodiments, the device that comprises the bidirectional switch is an enhancement-mode (normally off) device, which prevents damage to the device or other circuit components in case of circuit failure by preventing any accidental turn on of the device. The device predominantly used for bidirectional switching in power converters is the silicon insulated gate bipolar transistor (Si IGBT). While IGBT's are capable of handling the power requirements of the power converter circuits in which they are used, the devices themselves are neither bidirectional nor planar, i.e., current flows vertically and in only one direction in an IGBT. Thus, the device requires a relatively complicated configuration to operate properly. Several common configurations of IGBT-based bidirectional switches are shown in FIG. 3. The more commonly used configurations consist of two anti-parallel IGBT's each in series with a blocking diode (FIGS. 3b and 3c), thus requiring a minimum of four discrete devices. A simpler configuration consists of two anti-parallel reverse blocking IGBT's (FIG. 3a); however, these devices are more expensive due to the complexity of their design (FIG. 3d) and tend to experience higher loss.